Central entry dual rotor cavitation

ABSTRACT

A method is described of mixing fluid materials, including solids and gases. The materials to be mixed are introduced between two cylindrical rotors mounted in parallel on a motorized shaft. The rotors have arrays of cavities on their cylindrical surfaces and rotate within close proximity to the interior of a cylindrical shell. Passage of the fluid between the rotating rotors and the interior surface of the cylindrical shell causes cavitation, which mixes the materials. The mixture is passed to outlets on the far sides of the rotors from the inlet. Apparatus is described for extending the flow path of the materials and thus increasing exposure to the cavitation process.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/000,116 filed May 19, 2014, which is incorporated by reference in itsentirety.

TECHNICAL FIELD

A cavitation device especially useful for mixing materials comprises twoparallel cylindrical rotors within a housing having an inner surfacesubstantially concentric with the cylindrical surfaces of the rotors,the rotors including a plurality of bores or cavities on their surfaces.In a method of mixing, a fluid inlet to the space between the rotorsinjects one or more fluid components for mixing, and two outlets removeit after following a flow path through the cavitation zones. The deviceand method are especially useful for mixing drilling muds, fracturingfluids, and other oil field fluids. One or more optional discs may bedeployed in parallel to the rotors to augment the use of viscous drag toturn the rotors and moderate energy consumption while optimizing thedesirable cavitation and mixing effects.

BACKGROUND OF THE INVENTION

Cavitation devices of the type disclosed by Griggs (U.S. Pat. Nos.5,188,090, 5,385,298, and 5,957,122), Hudson et al U.S. Pat. No.6,627,784, Wyszomerski U.S. Pat. No. 3,198,191, Selivanov U.S. Pat. No.6,016,798, Thoma U.S. Pat. Nos. 7,089,886, 6,976,486, 6,959,669,6,910,448, and 6,823,820, Costa et al U.S. Pat. No. 6,595,759, Giebeleret al U.S. Pat. Nos. 5,931,153 and 6,164,274, and Archibald et al U.S.Pat. No. 6,596,178 are designed to mix and heat fluids passing throughthem. A cavitation zone is formed between a rotating cylindrical orother surface and a conforming housing surface, the rotating surfacecontaining numerous cavities. The cavitation effect achieved by themini-violent turbulence in and around the cavities is known. The Griggsand Hudson et al cavitation devices described in the patents above, inparticular, have been used successfully in commerce. However, somefluids are more challenging than others. Many applications requirehandling dense materials with throughput rates beyond the capabilitiesof the existing devices and methods.

I have found that the prior art designs and methods do not efficientlyaccount for the fluid properties of the materials to be mixed, orefficiently direct the flow patterns within the devices in many mixingapplications.

Combined fluids (a) having high viscosities, and/or (b) that are denseor heavy, and/or (c) that include high concentrations of solids, areoften found not to be well mixed using a desired flow rate through thecavitation devices described in the above patents. Prior art devices andmethods are not able to overcome the negative effects of viscous dragsometimes even as exerted by fluids having relatively low viscosities.Both the designs of the devices and the methods of using them arewasteful of energy and limit the potential of the cavitation phenomenonas applied to virtually any fluid or combination of fluids to be mixed.

Hudson et al U.S. Pat. No. 6,627,784 in particular introduces thematerials to be mixed through two inlet ports directing the floworthogonal to its rotor and removes it from the center of the singlerotor's cylindrical periphery, in an attempt to balance the flow. Thisconstruction and method have been found to generate excessive drag, iswasteful of energy, and is incapable of achieving an acceptable mix athigh fluid flow rates.

SUMMARY OF THE INVENTION

My technique utilizes two parallel cavitation rotors separated by aspace adequate in width to accommodate the incoming fluid and othermaterial(s) to be mixed. In prior devices, such as described in theHudson et al '784 patent mentioned above, turbulence and drag wasgenerated when the incoming fluid was more or less directed toward theface of the rotor, thus tending to retard rotation. By directing it onthe periphery of the housing into a central space between two separaterotors, in one variation also substantially tangential to the housing'sinternal surface, the viscous drag effect of the incoming material onthe side of the rotor is exerted in a positive manner, generally incooperation with the rotational direction.

When viewed from a face, or end wall, of the housing, the outlet for themixed fluid may beneficially be placed as much as 360 degrees from theinlet, thus beneficially varying the exposure of the fluid to thecavitation process. Typically, the flow path of the material will besuch that it will be transported once through the cavitation zone,although the velocity of the cylindrical surface of the rotor in myinvention may be considerably higher than the velocity of the fluidpassing through the cavitation zone, thus further enhancing thecavitation effect.

In a variation of the invention, a disc is fixed to the shaft betweenthe two parallel rotors. By also utilizing viscous drag of the incomingmaterial in a positive manner, the disc will also assist in turning therotors and assuring flow of the fluid into the cavitation zone.

In another variation, radial ribs may be included on the faces of therotors, on the central disc, or on both.

The invention includes a method of mixing materials comprisingintroducing the materials to a centrally located peripheral inlet of thedual-rotor cavitation device described above, rotating the rotors tocreate cavitation in the materials, and removing the mixture therebycreated from two side, or lateral, outlets of the cavitation device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows, with portions in section, a basic design of my cavitationdevice invention including an optional central disc.

FIG. 2 is also a partially sectional view of the apparatus, especiallyto illustrate the flow patterns within it.

FIG. 3 is a side view of the invention to illustrate tangential feed.

FIG. 4 shows optional radial ribs which may be used on either the rotorsor the optional disc or both.

In FIG. 5, a novel configuration of an inlet and two outlets is shown.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, rotors 10 and 11 are fixedly mounted on shaft12. One end of shaft 12 is turned by a motor not shown. Shaft 12 passesthrough, with appropriate bearings not shown, housing walls (sometimesherein called faces) 16 and 17, depicted as planar, although theexterior may assume other shapes. Together with cylindrical shell 15,housing walls 16 and 17 form a housing for the two rotors 10 and 11. Thehousing thus formed is sealed except for inlet 18 and outlets 19 and 20.By the term “cylindrical shell” I mean the curved part of the generallycylindrical shape of the housing. It will be understood that theexterior may assume other shapes but it is the interior surface of thecylindrical shell portion of the housing that functions to form thecavitation zones 14.

Rotors 10 and 11 have cavities 13 on their cylindrical surfaces. Rotors10 and 11 are positioned so that, when turned, they maintain acavitation zone 14 between the rotors and cylindrical shell 15. Fluidentering through inlet 18, flowing into the cylindrical shell 15,proceeds normally in the same direction the rotors 10 and 11 are turninguntil it is flung into the cavitation zone 14 (see the more detailedexplanation in FIG. 2), ultimately leaving through outlets 19 and 20.The mixed material from outlets 19 and 20 may be combined in a conduitnot shown or in a tank not shown; in the case of drilling mud and manyother materials, it will ready for immediate use.

Also shown in FIG. 1 is an optional disc 21, fixed to shaft 12 so itwill turn with shaft 12 and rotors 10 and 11. Optional disc 21 willexert a positive viscous drag effect on the fluid entering the devicethrough inlet 18, assisting in turning the rotors 10 and 11, therebyfurther assisting the cavitation process.

As is known in the art, a fluid passing through a cavitation zone suchas cavitation zone 14 between the rotating cavitation rotors 10 and 11and cylindrical wall 15 will be thoroughly mixed. As it moves throughthe cavitation zone 14, the fluid flows into cavities 13 but isimmediately ejected by centrifugal force, creating mini-vacuums in thecavities, which causes the fluid to implode into the cavities,generating heat and thoroughly mixing the ingredients. The process,however, is subject to a number of variables, such as the revolutionsper unit of time of the rotor, the size, depth and orientation of thecavities, the velocity of the cylindrical surface of the rotor (which isa function of its diameter), the distance between the surface of thecavitation rotor and the internal cylindrical surface of the housing,the flow rate of the fluid, and the viscosity, density and solidscontent of the fluid. This list does not exhaust the variables of thestructure and operation of the cavitation device, but my invention isdesigned especially to deal with variables in the fluid which canfrustrate the attempts of the operator to obtain a good mix.

FIG. 2 is similar to FIG. 1 but is intended to show the flow path ofmaterial through the dual rotor cavitation device. As indicated by thearrow in inlet 18, fluid enters through cylindrical shell 15 of thehousing centrally to the peripheries of rotors 10 and 11. It istherefore already in a position to move in a beneficial pattern into thecavitation zones 14 of both rotors. As indicated by flow path arrows 22,the fluid first encounters internal faces 23 and 24 of spinning rotors10 and 11, resulting in a viscous drag effect which assists in directingit to the cavitation zone 14. As indicated by arrows 22, the fluid mustpass across the width of the rotors 10 and 11 before passing out throughoutlets 19 and 20, completing its dual flow path.

In FIG. 2, outlets 19 and 20 are shown as in FIG. 1, placed about 180°from inlet 18 as viewed from a cross section of the cylindrical shell15. However, the outlets are advantageously placed at other positions inthe device, anywhere from 90° to 360° around the periphery of thehousing (cylindrical shell 15). Such variations are illustrated in FIGS.3 and 5.

FIG. 3 is a partially sectioned side view of the dual rotor cavitationdevice, highlighting the central peripheral inlet 18. One of the rotors,rotor 11, mounted on shaft 12, is shown from near the center of thedevice (face 24 in FIG. 2). Fluid is fed through inlet 18 in thedirection of rotation of the rotor 11, as indicated by the arrow labeled“Rotation.” The fluid makes contact with the entire face of rotor 11 butis soon moved into cavitation zone 14 where it is subjected to thecavitation process as described above. Outlet 20 is shown as a dottedcircle, as it is behind the rotor 11 in this view. However, one purposeof FIG. 3 is to show the positioning of optional alternative outlets 25,shown as a dotted circle about 90° from inlet 18, and outlet 26, shownas a solid circle about 270° on the flow path from inlet 18. Where anoutlet is positioned as is outlet 25, a corresponding outlet should beused on the equivalent side of rotor 10. Likewise, outlet 26 would haveits corresponding outlet also about 270° from inlet 18. The dual flowpaths would thus traverse three-fourths of the internal circumference ofthe cylindrical shell 15 while also crossing over the widths of bothcavitation rotors before being withdrawn. Such pairing of the outletswill help maintain pressure balance in the device but deviations may bemade if balance is of little consequence or if there are other ways ofcompensating.

FIG. 4 depicts a side view of the optional disc 21, showing especiallyoptional raised ribs 27. Raised ribs 27 are deployed substantiallyradially on both surfaces of optional disc 21. Similar raised, radialribs can be used on the inside surfaces of rotors 10 and 11—that is, onfaces 23 and 24 of the rotors, on the interior of the device, asindicated in FIG. 2. Such raised ribs will encourage the centrifugaldisposition of the fluid toward the cavitation zone. The ribs may becurved as well as straight as shown.

Comparative Example

The construction of the invention is unique, in one aspect among others,in that it has two cavitation rotors in parallel planes with an openspace between them and connected only by the shaft. But the inventionincludes a novel method also, in that it contemplates feeding theincoming materials to a central point between two separate rotors, onthe periphery of the housing, as shown variously in FIGS. 1, 2, 3, and5. In Table I below, this mode of operation, representing a method ofthe invention and employing a fluid flow path opposite that of the priorart, is labeled “Peripheral Entry.”

The direction of flow described by Hudson et al in U.S. Pat. No.6,627,784 is determined by introducing the materials to be mixed throughinlet ports on the sides, and collecting the mixture from an outlet portin the center of the cylindrical cover of the housing. On entering thedevice, the fluid impacts the sides of the single monolithic rotor, andis carried, apparently, 180 degrees by the rotor in the direction of itsrotation to the downstream, or lower pressure, outlet. This mode ofoperation is labeled “Orthogonal Entry” in Table I below because theentering fluid directly impacts the sides of the rotor at right angles.It should be noted that the Hudson et al monolithic rotor is builtspecifically to accommodate the flow pattern generated by its orthogonalentry—their “outlet port” is deliberately “aligned with the void 26” toprevent cavitation damage (column 6, lines 27-28). Void 26 is a portionof the '784 single, monolithic rotor having no cavities. It is not anopen space as in the present invention.

A machine constructed as illustrated in the drawings, particularly FIGS.1 and 2 hereof, but without optional disc 21, having two rotors 10 and11 each three inches wide and 16 inches in diameter, was used for thecomparison to demonstrate superiority of the method invention. Thedistance between the rotors was 4 inches. The ingredients for a typicalheavy oil field drilling mud, having a density of 8.5 pounds per gallon,were fed to the machine and it was operated to mix the ingredients.

The test was run at five different flow rates noted in Table I inbarrels per minute. For the “Orthogonal Entry” runs, the material wasintroduced to outlets 19 and 20 and removed from inlet 18. For the“Peripheral Entry” runs, the material was introduced to inlet 18 andremoved through outlets 19 and 20 (FIGS. 1 and 2), as contemplated bythe present invention. All runs were conducted on the same machine usingthe same batch of drilling mud materials. 300 amperes of current wereconstantly supplied for all runs. Revolutions per minute of the motor,and therefore the two rotors, was recorded, as was the voltage consumed.Tip speed, the velocity of the periphery of the rotors, was calculatedfrom the RPMs. A centrifugal force increase factor g was calculated fromthe differences in tip speed at each fluid flow rate.

TABLE I Orthogonal Entry Peripheral Entry Centrif. Force Barrels/ MotorTip Speed Motor Tip Speed Tip Speed Increase, minute RPM VoltageFeet/sec. RPM Voltage Feet/sec. Diff., % % g 1 3200 402 223.3 3233 410225.6 1.02 1.04 2 3050 387 212.8 3202 410 223.4 4.75 22.56 3 3034 382211.7 3200 406 223.3 5.2 27.04 4 3016 382 210.4 3200 409 223.3 5.7833.41 5 3013 382 210.2 3190 404 222.6 5.57 31.02

The amount of time consumed by the mixing operation is very important,as the operators often need a large quantity of drilling fluid on littlenotice and a fresh mix is superior to one which may have settledsomewhat. It is notable, therefore, that the tip speed in the operationof the invention method (Peripheral Entry) was reduced only by threefeet per second at 5 bpm compared to 1 bpm, while the orthogonal entrymode resulted in a reduction of 13.1 feet per second. The OrthogonalEntry method exhibited a clearly reduced tip speed as the flowincreased. Also it should be noted that for all runs, the PeripheralEntry method consistently drew higher voltages, which is an indicator ofhigher energy input to the cavitation zone, resulting in consistentlybetter mixed material. The invention method is certainly not limited toa flow rate of 5 barrels per minute or any particular tip speed incombination with a particular fluid flow rate. My invention isbeneficial at 1 barrel per minute or less and at flow rates greater than5 gallons per minute.

The centrifugal force factor has been calculated because centrifugalforce increases as the square of the velocity of a point on theperiphery of the rotors. The factor “Centrif. Force Increase, % g” inTable I is the square of the increase in tip speed in the PeripheralEntry method as compared to the Orthogonal Entry method for the notedmix flow rate through the unit. Differences in g of 33.41% at 4 barrelsper minute and 31.02% at 5 barrels per minute are manifested in muchmore efficient cavitation at those flow rates and therefore much bettermixing.

The invention method thus not only enables significantly greater energyconversion, but also much more efficient cavitation at the challengingflow rates of 4-5 barrels per minute of a drilling fluid.

Referring now to FIG. 5, a housing comprising housing wall 16 andcylindrical shell 15 encloses cavitation rotors 10 and 11 mounted onshaft 12 substantially as in FIGS. 1 and 2. Optional disc 21 is alsoshown as in FIGS. 1 and 2. Inlet 18 is set to introduce fluidingredients tangentially and centrally on the periphery of cylindricalshell 15. The fluid will circulate through the cavitation zone 14 (FIGS.1 and 2) more or less as shown in FIG. 2, but will leave the devicethrough outlets 30 and 31 not on the side walls as in FIG. 2 but alsotangential to the periphery of cylindrical shell 15. Outlets 30 and 31are not only tangential to the curved surface of the housing'scylindrical shell 15, but also may be said to be laterally disposed oncylindrical shell 15, in contrast to the centrally disposed inlet 18.Outlets 30 and 31 may join in a “Y” configuration as shown to form asingle outlet 32. The “Y” connection reduces back pressure andturbulence as compared to a “T” connection. A “Y” connection is alsobeneficial for outlets 19 and 20 in FIGS. 1 and 2.

While the invention has utilized a device having cavitation rotors of 16inches in diameter and three inches wide, it should be understood thatthese dimensions can be varied considerably within the scope of theinvention. Likewise, in the absence of a disc such as optional disc 21,the distance between the rotors can vary from the width of the inlet tothree or four times the width of the inlet depending on the viscosity ofthe fluid, in order to take advantage of the viscous drag pumping effecton the rotor sides, which helps propel the fluid into the cavitationzone 14. The number of cavities, their depth, their shape, theirinclination, and the pattern of their arrays (including the width of therotors) can be varied considerably within the scope of the invention, ascan the distance between the interior surface of the cylindrical housingand the rotors, specifically the height of the cavitation zone 14.

The invention is especially useful for heavy and viscous materials withand without significant solids content. Oil field drilling muds, forexample, may vary in density up to 18 pounds per gallon or more whilealso being quite viscous, and it is with this in mind that the inventionhas been developed and for which it is known to be especially useful.Oil field fluids (by which I intend to include drilling fluids,fracturing fluids and completion fluids used in gas production) includedrilling, fracturing, completion, and other fluids used in theproduction of hydrocarbons from the earth. The invention is applicableto a wide variety of fluids including for the mixing of polymers,solids, and gases with liquids both aqueous and nonaqueous.

The invention has been described consistently with the rotation of therotors in the same direction as the flow of the fluid through thedevice. Nevertheless, it should be understood that the rotors can beoperated in the opposite direction—for example, in FIG. 3, the arrow forrotation would be reversed although the fluid flow pattern would be asdescribed.

Also, more than one disc 21 can be used. Two, three, or more such discscan be fixed to shaft 12 to further enhance the efficiency of the unit.

Thus, my invention includes a method of mixing materials comprisingintroducing materials to be mixed between two cavitation rotors in ahousing comprising a cylindrical shell, the cylindrical shell forming acavitation zone with each of the cavitation rotors, rotating thecavitation rotors to create cavitation in the cavitation zones, andwithdrawing the materials so mixed from the housing after they havepassed through the cavitation zones. The method is useful, among otherpurposes, for mixing drilling, fracturing and completion fluids in therecovery of hydrocarbons from the earth.

The invention also includes a method of mixing materials comprising (a)introducing the materials to be mixed to the inlet of a cavitationdevice, the cavitation device comprising two cavitation rotors mountedin parallel on a shaft and enclosed in a cylindrical housing forming acavitation zone with the rotors, (b) rotating the rotors to createcavitation in the materials, thereby mixing the materials, and (c)removing the mixture thereby created from the cavitation device throughtwo outlets, wherein the inlet is located centrally and peripherally onthe cylindrical housing and the outlets are located laterally on saidhousing.

Also included in the invention is a cavitation device comprising (a) twocylindrical rotors in parallel planes, the rotors each having aplurality of cavities on its cylindrical surface (b) a sealed housingenclosing rotors, the housing having two end walls and a cylindricalshell positioned to create a cavitation zone between each rotor and thehousing when the rotors are rotated, (c) a shaft passing through thehousing walls and the rotors for rotating the rotors, (d) an inlet forintroducing fluid to the housing, the inlet positioned to inject fluidthrough the cylindrical shell and between the rotors and (e) two outletsfor the fluid, the outlets being positioned at least 200 degrees withrespect to said cylindrical shell from the inlet, the outlets positionedalso to create flow paths for the fluid through the cavitation zonesbefore reaching the outlets.

1. Method of mixing materials comprising introducing materials to be mixed between two cavitation rotors in a housing comprising a cylindrical shell, said cylindrical shell forming a cavitation zone with each of said cavitation rotors, rotating said cavitation rotors to create cavitation in said cavitation zones, and withdrawing the materials so mixed from said housing after they have passed through said cavitation zones.
 2. Method of claim 1 wherein said materials include at least one fluid.
 3. Method of claim 1 wherein said materials for mixing comprise oil field fluid materials.
 4. Method of claim 3 wherein said oil field fluid is a drilling fluid.
 5. Method of claim 3 wherein said oil field fluid is a fracturing fluid.
 6. Method of claim 3 wherein said oil field fluid is a completion fluid.
 7. Method of claim 1 wherein said materials to be mixed are introduced substantially tangentially to said cylindrical shell.
 8. Method of claim 1 wherein said materials so mixed are withdrawn through two outlets substantially tangent to said cylindrical shell.
 9. Method of claim 1 wherein said materials traverse at least 90 degrees of the cylindrical surface of said cylindrical shell.
 10. Method of claim 1 wherein said materials are introduced to and withdrawn from said housing at a flow rate of at least 4 barrels per minute.
 11. Method of claim 1 wherein said cavitation rotors are fixedly mounted on a shaft and wherein at least one disc is also mounted on said shaft between said cavitation rotors.
 12. A cavitation device comprising (a) two cylindrical rotors in parallel planes, said rotors each having a plurality of cavities on its cylindrical surface (b) a sealed housing enclosing rotors, said housing having two end walls and a cylindrical shell positioned to create a cavitation zone between each rotor and said housing when said rotors are rotated, (c) a shaft passing through said housing walls and said rotors for rotating said rotors, (d) an inlet for introducing fluid to said housing, said inlet positioned to inject fluid through said cylindrical shell and between said rotors and (e) two outlets for said fluid, said outlets being positioned at least 200 degrees with respect to said cylindrical shell from said inlet, said outlets positioned also to create flow paths for said fluid through said cavitation zones before reaching said outlets.
 13. The cavitation device of claim 12 wherein said two outlets are positioned 360 degrees from said inlet.
 14. The cavitation device of claim 12 wherein said inlet is positioned to inject fluid substantially tangentially to said cylindrical shell.
 15. The cavitation device of claim 12 wherein and said outlets are positioned to remove fluid substantially tangentially with respect to said cylindrical shell.
 16. The cavitation device of claim 12 including at least one disc mounted on said shaft between said rotors.
 17. The cavitation device of claim 16 including radial ribs on said at least one disc.
 18. The cavitation device of claim 12 including a motor for rotating said shaft.
 19. Method of mixing materials comprising (a) introducing said materials to be mixed to the inlet of a cavitation device, said cavitation device comprising two cavitation rotors mounted in parallel on a shaft and enclosed in a cylindrical housing forming a cavitation zone with said rotors, (b) rotating said rotors to create cavitation in said materials, thereby mixing said materials, and (c) removing the mixture thereby created from said cavitation device through two outlets, wherein said inlet is located centrally and peripherally on said cylindrical housing and said outlets are located laterally on said housing.
 20. Method of claim 19 including merging said outlets into a single conduit. 